Systems for converting an image, such as the characters of an image-bearing document, into electrical signals which can either be stored in a memory for later recall or which can be transmitted to a remote location over, for example, telephone communication or similar systems, are well known in the image reproduction art. Systems of this type have generally been referred to as line scanners. In one type of line scanner, the document is held stationary and a photodetector or an array of photodetectors are scanned across each line of the image-bearing document along with a localized light source. In another type of scanner, the array of photodetectors and light source are held stationary while the document is moved therepast. In both types of systems, as the image-bearing document is scanned, the high optical density or dark portions of the document reflect less light from the light source for reception by the photodetectors than the low optical density or light portions of the document. As a result, the high and low optical density portions of the image-bearing document can be contrasted by the photodetectors for generating electrical signals representative of the image on or other surface characteristic of that document.
While systems of the type described above have been generally successful in fulfilling their intended purposes and have found commercial acceptance, these systems have heretofore exhibited several deficiencies. For one thing, due to the relative motion which must exist between the document and the photodetectors, a large static electrical charge is built-up on the document being scanned. Therefore, precautions must be undertaken to prevent that static charge from inducing an electrical charge in the spacedly positioned array of photodetectors, which induced charge would be capable of deleteriously affecting and possibly fatally damaging said photodetectors. By utilizing the photodetector structure detailed in commonly assigned U.S. patent application Ser. No. 912,477, the problem associated with static charge induction has been obviated.
Another deficiency which is present in prior art contact line scanning systems arises due to the constant abrasive contact which the array of light sensitive elements incurs due to the movement of the image-bearing document therepast. Similarly, the array of light sensitive elements may be employed in an environment wherein acidic, corrosive or other deleterious gases could detrimentally affect the semiconductor alloy material from which those elements are fabricated and hence degrade the performance of the array. By depositing any of the transparent, hard protective coatings described in commonly assigned U.S. patent application Ser. No. 912,476 immediately atop said elements, the problems associated with such abrasive and corrosive environments have been substantially eliminated.
Since the previously encountered problems of static charge build-up and paper abrasion have been eliminated in a manner which protects the light sensitive elements of a contact imaging photosensor array, it now becomes commercially feasible to fabricate contact image scanners wherein relative motion exists between the image-bearing document and the array of light sensitive elements. It is therefore the major object of the present invention to provide a contact-type image scanning apparatus in which the image-bearing document is moved in a proximity focusing manner past the light sensitive elements of a photosensor array without detrimentally affecting said elements.
Other objects and advantages of the subject invention will become apparent from a perusal of the detailed description of the invention, the drawings and the claims which follow.